1 files changed, 123 insertions, 0 deletions
diff --git a/lib/Plugins.Essentials/src/FilePathCache.cs b/lib/Plugins.Essentials/src/FilePathCache.cs
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+++ b/lib/Plugins.Essentials/src/FilePathCache.cs
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+/*
+* Copyright (c) 2024 Vaughn Nugent
+* 
+* Library: VNLib
+* Package: VNLib.Plugins.Essentials
+* File: FilePathCache.cs 
+*
+* FilePathCache.cs is part of VNLib.Plugins.Essentials which is part 
+* of the larger VNLib collection of libraries and utilities.
+*
+* VNLib.Plugins.Essentials is free software: you can redistribute it and/or modify 
+* it under the terms of the GNU Affero General Public License as 
+* published by the Free Software Foundation, either version 3 of the
+* License, or (at your option) any later version.
+*
+* VNLib.Plugins.Essentials is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+* GNU Affero General Public License for more details.
+*
+* You should have received a copy of the GNU Affero General Public License
+* along with this program.  If not, see https://www.gnu.org/licenses/.
+*/
+
+using System;
+using System.Diagnostics;
+using System.Collections.Concurrent;
+using System.Diagnostics.CodeAnalysis;
+
+namespace VNLib.Plugins.Essentials
+{
+
+    /// <summary>
+    /// Represents a cache store for translated file paths to avoid 
+    /// path probing and file system syscalls
+    /// </summary>
+    internal abstract class FilePathCache
+    {
+
+        public abstract bool TryGetMappedPath(string filePath, [NotNullWhen(true)] out string? cachedPath);
+
+        /// <summary>
+        /// Attempts to store a path mapping in the cache store
+        /// </summary>
+        /// <param name="requestPath">The requested input path</param>
+        /// <param name="filePath">The filesystem path this requested path maps to</param>
+        public abstract void StorePathMapping(string requestPath, string filePath);
+
+        /// <summary>
+        /// Creates a new cache store with the specified max age. If max age is zero, the 
+        /// cache store will be disabled.
+        /// </summary>
+        /// <param name="maxAge">The max time to store the cahced path reecord</param>
+        /// <returns>The cache store</returns>
+        public static FilePathCache GetCacheStore(TimeSpan maxAge)
+        {
+            return maxAge == TimeSpan.Zero 
+                ? new DisabledCacheStore() 
+                : new DictBackedFilePathCache(maxAge);
+        }
+
+        /*
+         * A very basic dictionary cache that stores translated paths
+         * from a request input path to a filesystem path.
+         * 
+         * This must be thread safe as it's called in a multithreaded context.
+         */
+        private sealed class DictBackedFilePathCache(TimeSpan maxAge) : FilePathCache
+        {
+            private readonly ConcurrentDictionary<string, CachedPath> _pathCache = new(StringComparer.OrdinalIgnoreCase);
+
+            ///<inheritdoc/>
+            public override bool TryGetMappedPath(string filePath, [NotNullWhen(true)] out string? cachedPath)
+            {
+                if (_pathCache.TryGetValue(filePath, out CachedPath cp))
+                {
+                    //TODO: Implement a cache eviction policy
+                    cachedPath = cp.Path;
+                    return true;
+                }
+
+                cachedPath = null;
+                return false;
+            }
+
+            ///<inheritdoc/>
+            public override void StorePathMapping(string requestPath, string filePath)
+            {
+                ArgumentException.ThrowIfNullOrWhiteSpace(requestPath);
+
+                //Cache path is an internal assignment. Should never be null
+                Debug.Assert(filePath is not null);
+
+                //TODO: Implement a cache eviction policy
+                _pathCache[requestPath] = new CachedPath { Path = filePath, LastStored = DateTime.MinValue.Ticks };
+            }
+
+            private struct CachedPath
+            {
+                public required string Path;
+                public required long LastStored;
+            }
+        }
+
+        /*
+         * A cache store that does nothing, it always misses and will 
+         * cause a normal file fetch 
+         */
+        private sealed class DisabledCacheStore : FilePathCache
+        {
+            ///<inheritdoc/>
+            public override void StorePathMapping(string requestPath, string filePath)
+            { }
+
+            ///<inheritdoc/>
+            public override bool TryGetMappedPath(string filePath, [NotNullWhen(true)] out string? cachedPath)
+            {
+                cachedPath = null;
+                return false;
+            }
+        }
+    }
+}